The paradox of MHC-DRB exon/intron evolution: α-helix and β-sheet encoding regions diverge while hypervariable intronic simple repeats coevolve with β-sheet codons

Twenty-one different caprine and 13 ovine MHC-DRB exon 2 sequences were determined including part of the adjacent introns containing simple repetitive (gt)_n(ga)_m elements. The positions for highly polymorphic DRB amino acids vary slightly among ungulates and other mammals. From man and mouse to ungulates the basic (gt)_n(ga)_m structure is fixed in evolution for 7 × 10⁷ years whereas ample variations exist in the tandem (gt)_n and (ga)_m dinucleotides and especially their degenerated derivatives. Phylogenetic trees for the -helices and -pleated sheets of the ungulate DRB sequences suggest different evolutionary histories. In hoofed animals as well as in humans DRB -sheet encoding sequences and adjacent intronic repeats can be assembled into virtually identical groups suggesting coevolution of noncoding as well as coding DNA. In contrast a-helices and C-terminal parts of the first DRB domain evolve distinctly. In the absence of a defined mechanism causing specific, site-directed mutations, double-recombination or gene-conversion-like events would readily explain this fact. The role of the intronic simple (gt)_n(ga)_m repeat is discussed with respect to these genetic exchange mechanisms during evolution.     

Netuptake of sulphate and its transport to the shoot in tobacco plants fumigated with H2S or SO2

In tobacco plants the net uptake of sulphate and its transport to the shoot were determined after cultivation with low, normal, and high sulphate supply. The relative amount of the sulphate taken up that was transported to the shoot was used as a measure of xylem loading. Net uptake of sulphate and its transport to the shoot were low in tobacco plants grown with low sulphate, and high in plants cultivated with high sulphate. Xylem loading, however, was relatively low in tobacco plants grown with high sulphate and relatively high in tobacco plants grown with low sulphate supply. Pre-culture in low sulphate containing nutrient solution also resulted in a high proportion of the absorbed sulphate being transported into the xylem if normal sulphateconcentration was supplied afterwards. Fumigation with H₂S or SO₂ reduced net uptake of sulphate in tobacco plants grown with normal, but not with high sulphate supply. Sulphate transport to the shoots was diminished by H₂S or SO₂ fumigation in tobacco plants grown with normal and high sulphate supply. Also the relative amount of the sulphate taken up that was transported to the shoot was lowered by fumigation with H₂S or SO₂ in tobacco plants grown with normal sulphate supply. Apparently, the diminished sulphate transport to the shoot upon H₂S or SO₂ fumigation can only partially be explained by a smaller sulphate uptake. Sulphur nutrition of tobacco plants also seems to be controlled by xylem loading of sulphate. The possible role of glutathione as a signal regulating sulphur nutrition of tobacco plants upon fumigation with H₂S and SO₂ is discussed.     

Genetics and development of morphological and physiological characters of male sterility in Oenothera

Summary Male sterility in Oenothera is influenced by two nuclear genes,fr andster. Their function is independent of the plastomes. Development of anthers, fertile and sterile male, was studied by electron microscopy and histochemical methods. Both genes act on lipid metabolism but at different developmental stages. Infr/fr homozygotes the disturbance is expressed as a lack of sporopollenin in the exine, while amorphous lipid material is deposited in the loculus. Inster/ster homozygotes sporopollenin is formed normally in the endexine but the paracristalline structure of the ektexine is missing. In both mutants the disturbance leads to complete destruction of the pollen grain. The deviation from fertile pollen development is correlated with abnormalities of the tapetum and outer cell layers of the anther wall.     

Reduced sulphur allocation from three-year-old needles of Norway spruce (Picea abies [Karst] L.)

The ³⁵S-labelled sulphur compounds glutathione, cysteine, and-glutamylcysteine were fed to 6-year-old spruce trees via thecut surface of a single 3-year-old needle. After 1–3 hexposure, uptake of the radiotracer into the fed needle, exportinto other parts of the plant and distribution between needles,bark and wood along the transport path were analysed. Uptakeof cysteine into the exposed needle was one order of magnitudeand uptake of -glutamylcysteine two orders of magnitude lowerthan that of glutathione. Independent of the thiol applied,the current year's sprouts were the preferential sinks of exported³⁵S. Transport towards basipetal parts of the twig amountedto less than 10% of total ³⁵S export in all cases. After feeding³⁵S-cysteine and ³⁵S--glutamylcysteine, ³⁵S-glutathione wasfound along the transport path, in particular in distant partsof the twig. This was also observed when ³⁵S-GSH was fed. Thisresult confirms the significance of glutathione as the majorlong-distance transport form of reduced sulphur in spruce twigs.In xylem sap of trunk sections of spruce, cysteine rather thanglutathione was the main thiol. Cysteine concentrations in thexylem sap of the trunk amounted to 260–500 nmol l^–1.Glutathione concentrations were 2–5 times and -glutamylcysteineconcentrations 4–16 times lower than those of cysteine. Key words: Glutathione, -glutamylcysteine, cysteine, long-distance transport     

Callose pattern and polarization phenomena in the ovules in the F2-hybrids betweenOenothera hookeri andOe. suaveolens

The pattern of callose formation in meiotic cell walls and the order of megaspore degeneration and polarity during embryo sac development are investigated in F₂-plants ofOe. hookeri ×suaveolens and the reciprocal cross. All investigated characters are variable between the ovules in the same ovary. Plants differ in the frequency of the types of callose pattern and polarity of the embryo sacs. In segregating progenies different combinations of both characters are found. The genetic basis of the polarity phenomena during the embryo sac development is discussed. In our material no correlation can be seen between the callose pattern in the surrounding wall of the meiotic cell and the development of polarity in the later stages.     

Identification of a membrane-bound, glycol-stimulated phospholipase A2 located in the secretory granules of the adrenal medulla

Chromaffin granule membranes prepared from bovine adrenal medullae showed Ca2(+)-stimulated phospholipase A2 (PLA2) activity when assayed at pH 9.0 with phosphatidylcholine containing an [14C]-arachidonyl group in the 2-position. However, the activity occurred in both soluble and particulate subcellular fractions, and did not codistribute with markers for the secretory granule. PLA2 activity in the granule membrane preparation was stimulated dramatically by addition of glycerol, ethylene glycol, or poly(ethylene glycol). This glycol-stimulated PLA2 activity codistributed with membrane-bound dopamine beta-hydroxylase, a marker for the granule membranes, through the sequence of differential centrifugation steps employed to prepare the granule membrane fraction, as well as on a sucrose density gradient which resolved the granules from mitochondria, lysosomes, and plasma membrane. The glycol-stimulated PLA2 of the chromaffin granule was membrane-bound, exhibited a pH optimum of 7.8, retained activity in the presence of EDTA, and was inactivated by p-bromophenacyl bromide. When different 14C-labeled phospholipids were incorporated into diarachidonylphosphatidylcholine liposomes, 1-palmitoyl-2-arachidonylphosphatidylcholine was a better substrate for this enzyme than 1-palmitoyl-2-oleylphosphatidylcholine or 1-acyl-2-arachidonyl-phosphatidylethanolamine, and distearoylphosphatidylcholine was not hydrolyzed.     

Production of sorbitol and gluconic acid by permeabilized cells of Zymomonas mobilis

Summary Zymomonas mobilis is able to convert glucose and fructose to gluconic acid and sorbitol. The enzyme, glucose-fructose oxidoreductase, catalysing the intermolecular oxidation-reduction of glucose and fructose to gluconolactone and sorbitol, was formed in high amounts [1.4 units (U)·mg^-1] when Z. mobilis was grown in chemostats with glucose as the only carbon source under non-carbon-limiting conditions. The activity of a gluconolactone-hydrolysing lactonase was constant at 0.2 U·mg^-1. Using glucose-grown cells for the conversion of equimolar fructose and glucose mixtures up to 60% (w/v), a maximum product concentration of only 240 g·1^-1 of sorbitol was found. The gluconic acid accumulated was further metabolized to ethanol. After permeabilizing the cells using cationic detergents, maximum sorbitol and gluconic acid concentrations of 295 g·1^-1 each were reached; no ethanol production occurred. In a continuous process with -carrageenan-immobilized and polyethylenimin-hardened, permeabilized cells no significant decrease in the conversion yield was observed after 75 days. The specific production rates for a high yield conversion ( > 98%) in a continuous two-stage process were 0.19 g·g^-1·h^-1 for sorbitol and 0.21 g·g^-1·h^-1 for gluconic acid, respectively. For the sugar conversion of cetyltrimethylammonium bromide-treated -carrageenan-immobilized cells a V _max of 1.7 g·g^-1·h^-1 for sorbitol production and a K _m of 77.2 g·1^-1 were determinedOffprint requests to: B. Rehr     

Mechanism of coumarin action: sensitivity of vitamin K metabolizing enzymes of normal and warfarin-resistant rat liver

The in vitro effects of two coumarin anticoagulants, warfarin and difenacoum, on rat liver microsomal vitamin K dependent carboxylase, vitamin K epoxidase, vitamin K epoxide reductase, and cytosolic vitamin K reductase (DT-diaphorase) from the livers of normal and a warfarin-resistant strain of rats have been determined. Millimolar concentrations of both coumarins are required to inhibit the carboxylase and epoxidase activities in both strains of rats. Sensitivity of DT-diaphorase to coumarin inhibition differs when a soluble or liposomal-associated substrate is used, but the diaphorases isolated from both strains of rats have comparable sensitivity. The anticoagulant difenacoum is an effective rodenticide in the warfarin-resistant strain of rats, and the only enzyme studied from warfarin-resistant rat liver that demonstrated a significant differential inhibition by the two coumarins used was the vitamin K epoxide reductase. This enzyme also showed the greatest sensitivity to coumarin inhibition among the enzymes studied. These results support the hypothesis that the physiologically important site of action of coumarin anticoagulants is the vitamin K epoxide reductase.     

Multinucleate Sertoli cells in aged human testis

Summary The present investigation documents morphological characteristics of human Sertoli cells of aged males. Testicular material was obtained from 35 patients (age 62–84 years) with carcinoma of the prostate who had received no previous anticancer therapy. As revealed by light and electron microscopy the appearance of the germinal epithelium showed great individual variations. In all cases examined, however, the occurrence of multinucleate Sertoli cells was a common finding. In seminiferous tubules with intact spermatogenesis these cells closely resembled the normally occurring variants, whereas they displayed features reminiscent of immaturity in the absence of germ cells. It is hypothesized that the nuclei of Sertoli cells in the special situation of aging may resume the capacity to divide, an ability normally restricted to immature cells. Thus, mitosis without subsequent cytokinesis might be an explanation for the formation of multinucleate Sertoli cells.The authors wish to thank Dr. R. Hubmann, Hamburg, for kindly supplying the testicular material. The excellent technical assistance of Mrs. E. Roosen-Runge, Mrs. E. Schäfer, and Mrs. A. Stromeyer is gratefully acknowledgedSupported by grants from the Deutsche ForschungsgemeinschaftPresented in part at the Kleinkonferenz der Deutschen Forschungsgemeinschaft, Schloß Auel, October 3–5, 1980     

Impaired negative cooperativity of the semisynthetic analogues human [LeuB24]- and [LeuB25]-insulins

Several semisynthetic analogues of human insulin were prepared by enzyme-assisted coupling of synthetic octapeptides to the C-terminal of porcine desoctapeptide insulin. We report the receptor-binding and biological properties of [Leu^B24]- and [Leu^B25]-insulins, one of which has the same sequence as a “mutant” insulin recently found in a diabetic patient (Tager, H. et al.(1979) Nature $\text{28}$:121–125). [Leu^B24]- and [Leu^B25]-insulins had, respectively, 8–12% and 0.9–1.1% of the binding affinity of human insulin, and 11% and 2.7% of its potency in stimulating lipogenesis in isolated rat fat cells. Neither one was an antagonist of the biological effects of native insulin. While the ability of [Leu^B24]-insulin to induce negative cooperativity was clearly impaired, that of [Leu^B25]-insulin was almost abolished. [Leu^B25]-insulin was also a potent antagonist of the negative cooperativity induced by native insulin.